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Annual pasture legume growth on acid soils iii effect of soil acidity on the growth of seedling subterranean clover (trifolium subterraneum cv. junee) and barrel medic (medicago truncatula cv. paraggio)

P.D. Cregan, H. McInerney1, K.R. Helyar and M. Conyers2

1 Riverina-Murray Institute of Higher Education, Wagga Wagga, NSW 2650
Agricultural Research Institute, Wagga Wagga, NSW 2650

In many pasture paddocks and experiments late autumn/winter growth responses following the use of lime are observed but not measured. Subsequent yield measurements in spring, particularly of the acid tolerant species subterranean clover (subclover) frequently indicate a lack of response to lime. Extra growth in autumn-winter may be important for livestock production and possibly pasture x herbicide and pasture x disease interactions. Seedling top and root growth were measured from selected treatments of a pasture species x acid/lime rate factorial experiment near Wagga Wagga, NSW in 1988.


The establishment details of this experiment at Borambola have been described previously. Measurements were made on subclover and barrel medic plots that were treated_o create a wide range of soil pH. The treatments 1 were: sulphur 240 kg ha (DH1 ); lime 0 ha (pH2); 0.75 t ha1 (pH3); 3.0 t ha-1 (pH4); and 6.0 t ha 1 (pH 5 ). Ten plants were sampled at random from each treatment in the four replicates of the experiment. Individual plants were washed, divided into tops and roots, oven dried and weighed. The tops were then ground for tissue Mn analysis.

Results and discussion

Subclover total plant weight, shoot:root ratio, and weight of plant tops were all significantly affected by soil pH treatment. This contrasted with spring and total yields where only the pH treatment was slightly lower yielding. Plants in treatments pH, pH and pH all exhibited symptoms of Mn toxicity and were above the critical level 3 reported by Simon et al.(1). The data indicate Mn toxicity was likely to be the dominant limitation to growth. Barrel medic yield responses to pH changes followed the same pattern recorded for spring and total growth and except for the most acid treatment tissue Mn levels were not high. Both Al and Mn toxicities are likely to be involved. Trends in shoot:root ratio indicate possible impairment of root function or photosynthetic activity with the more acid treatments.

1. Simon, A., Cradock, F.W. and Hudson, A.W. (1984). Plant and Soil 41:129-140.

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